EP3572149B1

EP3572149B1 - Preparation method for olefin epoxidation catalyst and applications thereof

Info

Publication number: EP3572149B1
Application number: EP18805296.3A
Authority: EP
Inventors: Lei Wang; Tongji WANG; Fei Ye; Lichao YANG; Guangquan Yi; Jiaoying CUI; Naibo CHU; Yuan Li; Weiqi Hua
Original assignee: Wanhua Chemical Group Co Ltd
Current assignee: Wanhua Chemical Group Co Ltd
Priority date: 2017-05-25
Filing date: 2018-05-24
Publication date: 2023-08-09
Anticipated expiration: 2038-05-24
Also published as: EP3572149A4; JP6830550B2; JP2020515406A; ES2955563T3; HUE063786T2; US11213811B2; EP3572149A1; CN107224993B; WO2018214931A1; CN107224993A; US20200147599A1

Description

TECHNICAL FIELD

The present invention relates to a preparation method for an olefin epoxidation catalyst, specifically a preparation method for a SiO₂-Ti-MeO-SiO₂ composite oxide catalyst and further relates to use of the catalyst in catalyzing propylene epoxidation to prepare propylene oxide.

BACKGROUND

Co-oxidation methods, also known as Halcon methods, are important methods for producing propylene oxide, comprising isobutane co-oxidation method (PO/TBA) and ethylbenzene co-oxidation method (PO/SM). First of all, peroxide is obtained by oxidizing isobutane or ethylbenzene respectively, then propylene oxide is obtained by oxidizing propylene, and tert-butyl alcohol or styrene is co-produced.
Co-oxidation methods overcome the disadvantages such as strong corrosiveness, large production of polluted water of the chlorohydrin method, and have advantages such as low product cost (co-products share the cost) and less environmental pollution. Co-oxidation methods have been developed rapidly around the world since the methods were industrialized in 1969. At present, the capacity of producing propylene oxide by a co-oxidation method accounts for about 55% of the total capacity in the world. In the co-oxidation methods, PO/SM process co-produces styrene, which is a chemical product produced in bulk and is an important monomer for synthesizing resin and rubber. Due to the relatively broad market of the co-product, this process is spreading faster and faster.
The PO/SM processes can be divided into homogeneous PO/SM processes and heterogeneous PO/SM processes according to the different catalysts used in the key procedures (epoxidation procedures) of the processes. The catalysts used in the epoxidation procedures of the heterogeneous PO/SM processes are Ti-SiO₂ composite oxide catalysts. The main steps of the preparation methods disclosed in US Patent Applications US3829392 and US2003166951A1 as well as Chinese Patent Applications CN1894030A and CN1720100A are as follows: a silica gel carrier was dried first, and then using N₂ or other inert gases to introduce titanium halide vapor into a reaction tube to react with silica gel (this step is called a chemical vapor deposition), high temperature calcination, and finally a catalyst was prepared through steps such as water washing. The catalyst prepared by this method has problems such as the Ti active center is easily lost during use, the catalyst activity decreases rapidly and the catalyst has a short life.
US2013/116454 discloses a preparation method for an olefin epoxidation catalyst, which comprises the following steps: (1) loading sodium (NaCl together with pluronic) onto a silica gel carrier (TEOS) during the hydrothermal synthesis to obtain sodium modified silica gel carrier A; (2) carrying out a drying treatment at 40°C (and calcining at 550°C) for the silica gel carrier A obtained in step (1); (3) carrying out a chemical vapor deposition for the dried silica gel carrier A using TiCl4 vapor to obtain a silica gel B, on which the sodium salt and the TiCl₄ are loaded; (4) calcining (600°C 7 hours) the silica gel B obtained in step (3) to obtain a silica gel C; (5) carrying out a water vapor washing (steam at 325°C) for the silica gel C obtained in step (4) to obtain a Ti-NaO-SiO₂ composite oxide and ; (8) carrying out a silylanization treatment for the Ti-NaO-SiO2 composite oxide obtained in step (5).
In order to solve the above problems, it is necessary to seek a new preparation method for propylene epoxidation catalyst to reduce the loss of Ti active center and improve the service life of the catalyst.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a preparation method for an olefin epoxidation catalyst. The olefin epoxidation catalyst prepared by the preparation method of the present invention can reduce the loss of Ti active center during use and improve the service life of the catalyst.
In the present invention, the catalyst is obtained with the method as defined in claim 1.
Another object of the present invention is to provide use of the catalyst (also referred to as a SiO₂-Ti-MeO-SiO₂ composite oxide catalyst) prepared by said method, the catalysts can be used as a catalyst for olefin epoxidation to produce an epoxide, especially a catalyst for propylene epoxidation to produce propylene oxide, and the catalyst not only has good catalyst activity, the catalyst also has high average selectivity to PO (propylene oxide).
The product codes "A", "B", "C", "D" appeared in the preparation method of the present invention do not have special meanings and are used as product codes only for ease of description. The Ti species described herein are terms commonly used in the art, the Ti species comprise tetra coordinate skeletal titanium, free titanium dioxide.
Further, in some specific embodiments, steps (3)-(8) are all carried out in the same reaction tube.
The auxiliary metal salt in step (1) of the present invention is one or more of Ce(NO₃)₃, Pr(NO₃)₃, Tb(NO₃)₃ and La(NO₃)₃. Using the amount of the metal oxide of the auxiliary metal salt for calculation, the auxiliary metal salt is added in an amount preferably ranging from 0.6-2.4 wt% based on the mass of the silica gel carrier. Said metal oxide refers to an oxide obtained from the decomposition after high-temperature calcination of the auxiliary metal salt, for example, the oxides corresponding to Ce(NO₃)₃, Pr(NO₃)₃, Tb(NO₃)₃ and La(NO₃)₃ are CeO₂, Pr₆O₁₁, TbO₂ and La₂O₃ respectively.
The impregnation method in step (1) can be an incipient-wetness impregnation method or other impregnation methods, and is not particularly limited as long as the method can load the auxiliary metal salt on the silica gel carrier. The specific operations of loading the auxiliary metal salt using an incipient-wetness impregnation method, for example, can be carried out as follows: first of all, measuring the water absorption per unit mass of the silica gel carrier, calculating the saturated water absorption of the silica gel carrier, and recording the saturated water absorption as a; weighing a certain amount of auxiliary metal salt and dissolving the salt in a grams of water, and recording the water solution as b solution; then evenly spraying b solution on the surface of the silica gel carrier, then allowing to settle, drying specifically, such as allowing to settle for 2-5 hours then drying at 80-120 °C; specific impregnation operations are conventional means in the art, and will not be described in detail.
An auxiliary metal salt is added in step (1) of the present invention, and the auxiliary metal salt is preferably one or more of Ce(NO₃)₃, Pr(NO₃)₃, Tb(NO₃)₃ and La(NO₃)₃. The purpose of adding an auxiliary metal salt is to utilize the alkalinity of the oxide formed from the auxiliary metal salt during the subsequent calcination process, thereby neutralizing the acidity of the free TiO₂ which is inevitably produced in step (4) and the subsequent steps, reducing self-decomposition reactions of peroxides and improving catalyst selectivity.
The silica gel carrier used in step (1) of the present invention is a C-type silica gel, and the specific shape thereof can be but is not limited to a spherical shape or a block etc., and there's no special requirement for the specific shape, for example, the silica gel can be but is not limited to an irregular blocky C-type silica gel. Preferably, the silica gel carrier used in step (1) has a specific surface area of 100-350 m²/g, an average pore diameter of 8-11 nm, a pore volume of 0.7-1.2 ml/g, a Na₂O impurity content of <100 ppm, a Fe₂O₃ impurity content of <500 ppm and a size of a spherical equivalent diameter of 0.5-2 mm.
The main purpose of drying in step (2) of the present invention is to remove free water in the silica gel carrier, preferred drying temperature is 150-240 °C and preferred drying time is 120 min - 240 min. Preferably, in step (2), the auxiliary metal salt modified silica gel carrier A obtained in step (1) is dried using a drying gas, and the drying gas used for drying can be any gas that does not react with silica gel, such as air or nitrogen; the drying in step (2) can be carried out specifically in a reaction tube, and the flow rate of the drying gas in the reaction tube is preferably 1.0-3.0 cm/s.
The step (3) of the present invention is a chemical vapor deposition, specifically, the chemical vapor deposition of this step can be carried out in a reaction tube. The titanium salt vapor, preferably TiCl₄ vapor in the vaporization tank is introduced into the reaction tube using an inert gas, preferably N₂. The TiCl₄ vapor interacts with the associated hydroxy on the surface of the silica gel to carry out the following reaction:

~O-Si-OH + TiCl₄ → ~O-Si-O-Ti-Cl

wherein Ti is loaded on the silica gel carrier in an amount ranges from 0.1-5.0 wt%, preferably 2.5-4.5 wt% based on the weight of the silica gel carrier (i.e., the amount of loaded Ti is calculated based on the weight of the silica gel carrier used in step (1)), the Ti described herein is based on the Ti element in the used titanium salt vapor. In some specific embodiments, the titanium salt is contained in a vaporization tank to provide titanium salt vapor, and the titanium salt vapor, preferably TiCl₄ vapor has a temperature of 137 °C - 150 °C, i.e. the titanium salt vapor is preheated to this temperature; the flow rate of the inert gas, preferably N₂ in the reaction tube is 0.05-2.0 cm/s, preferably 0.50-1.35 cm/s, the temperature of the reaction between the titanium salt vapor, preferably TiCl₄ vapor and the associated hydroxy on the surface of the silica gel is 150-300 °C, and the deposition time is 120-240 min.
In some preferred embodiments, the calcination carried out in N₂ atmosphere in step (4) of the present invention is carried out at a calcination temperature ranges from 450-700 °C, preferably 500-600 °C, the temperature is increased in a rate ranges from 1.5-3 °C/min, and the calcination time is 30-240 min, preferably 120-180 min, the flow rate of N₂ is 0.05-2.0 cm/s, preferably 1-2.5 cm/s. The main purpose of calcination is to introduce the Ti species adsorbed on the surface of the silica gel into the silica gel skeleton to form a tetra-coordinated skeletal Ti (or a Ti= O tetrahedron) active center, to stabilize the active center, and some of the Cl elements form HCl gas during calcination process and are removed from the surface of the silica gel carrier.
The step (5) of the present invention is water washing, and the purpose thereof is to remove the Cl element adsorbed on the surface of the silica gel carrier using water vapor, reducing or eliminating the influence of Cl element on the performance of the catalyst; the water washing process can be carried out specifically in the reaction tube. Preferably, a certain amount of water vapor is introduced into the reaction tube using an inert gas, preferably N₂, and the Cl element on the surface of the silica gel carrier is interacted with the water vapor to form HCl gas to be removed from the surface of the silica gel carrier. In some specific embodiments, the water vapor comes from a vaporization tank, which has a temperature of 100-200 °C (i.e., the water vapor is preheated to this temperature), preferably 120-180 °C; the water washing time is 180-240 min, and the flow rate of the inert gas, preferably N₂ is 1-2.5 cm/s. The molar ratio of water vapor to Ti is 20-150:1, preferably 50-100:1, and the amount of Ti in this molar ratio is based on the amount of the Ti element in the titanium salt vapor used in step (3); water washing with a preferred molar ratio of water vapor can remove Cl effectively and completely.
The step (6) of the present invention is also a chemical vapor deposition, and the main purpose thereof is to load an alkyl silicate, preferably tetraethyl orthosilicate onto the surface of the silica gel carrier. Preferably, the chemical vapor deposition of this step is carried out in a reaction tube, and an alkyl silicate vapor, preferably tetraethyl orthosilicate vapor is introduced into the reaction tube using an inert gas, preferably N₂; in some specific embodiments, the alkyl silicate vapor, preferably tetraethyl orthosilicate vapor comes from a vaporization tank that is heated to a temperature of 166-200 °C, the flow rate of the inert gas, preferably N₂ in the reaction tube is 0.05-2.0 cm/s, preferably 0.5-1.0 cm/s, the reaction temperature is 166-200 °C, the reaction time is 120-180 min, and the weight ratio of alkyl silicate, preferably tetraethyl orthosilicate to silica gel carrier is 0.5-1:1, the weight of the silica gel carrier in this weight ratio is based on the weight of the silica gel carrier used in step (1).
The purpose of the step (7) of the present invention is to calcine and remove the ligand alkyl ester in the alkyl silicate in air atmosphere, the ligand alkyl ester forms an oxycarbide and is then removed, a SiO₂ film (or a SiO₂ layer) is further formed on the surface of the silica gel carrier, and a SiO₂-Ti-MeO-SiO₂ sandwich structure is formed, which can protect Ti species, reducing (decreasing) the loss (loss rates) of Ti active centers, and improving the stability of the catalyst. In some preferred embodiments, in step (7), the calcination is carried out with a heating rate of 1.5-3 °C/min, a calcination temperature of 500-700 °C, a calcination time of 30-120 min, and the flow rate of air is 0.5-1 cm/s.
The step (8) of the present invention is a silylanization treatment, and the silylanization treatment can be specifically carried out in a reaction tube, a silylanization reagent vapor is introduced into the reaction tube using an inert gas, preferably N₂, and the chemical reaction is carried out as follows:

~O-Si-OH + Si(CH₃)₃-NH-Si(CH₃)₃ → ~O-Si-O-Si(CH₃)₃
The purpose of the silylanization treatment is to increase the hydrophobicity of the catalyst surface, reducing the decomposition ability of the catalyst to peroxide, and improving the selectivity of the catalyst; the silylanization reagent is preferably hexamethyl disilylamine, hexamethyl disilylamine which is used in an amount of 5 wt% - 15 wt% based on the weight of the silica gel carrier (i.e., based on the weight of the silica gel carrier used in step (1)); preferably, the temperature of hexamethyl disilylamine is 126-150 °C, the silylanization temperature is 200-300 °C, the flow rate of the inert gas, preferably N₂ in the reaction tube is 0.5-1 cm/s, and the silylanization time is 60-180 min.
The catalyst prepared by the preparation method of the present invention is used for catalyzing propylene epoxidation to prepare propylene oxide. The preferred process conditions are as follows: the reaction temperature is 40-120 °C, the pressure is 2-4.5 MPa (gauge pressure), the molar ratio of propylene to ethylbenzene hydroperoxide (EBHP) is 3-10:1, and the mass space velocity is 1-5 h^-1.
The present invention has the following advantageous effects:

(1) A layer of SiO₂ is further deposited on the surface of Ti-MeO-SiO₂ composite oxide by chemical vapor deposition, a layer of protective SiO₂ shell is formed, and a SiO₂-Ti-MeO-SiO₂ sandwich structure is formed, which can protect Ti species, reducing (decreasing) the loss (loss rates) of Ti active centers, and improving the stability of the catalyst; (2) by modifying the silica gel carrier though adding a metal auxiliary thereto, the metal auxiliary synergizes with Ti active centers to improve the activity and the selectivity to propylene oxide of the catalyst, the average selectivity of the catalyst to PO is up to 96.7%, which reduces the consumption of only propylene of PO products; (3) The process flow of the present invention is simple to control, easy to industrialize, and has great prospects for industrialization.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a schematic diagram showing the process flow of a catalyst preparation device.
Description of the reference signs: 1 represents a alkyl silicate vaporization tank, 2 represents a TiCl₄ vaporization tank, 3 represents a water and silylanization reagent vaporization tank; 4 represents an exhaust gas absorption tank; and 5 represents a reaction tube.

EMBODIMENTS

In order to understand the present invention better, the present invention will be further illustrated below with reference to the embodiments, but the content of the present invention is not limited thereto.
The Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES) used in the examples of the present invention was produced by Agilent Technologies, model 720 ICP-OES;

In the examples of the present invention, the content of PO (propylene oxide) in the reaction liquid and the exhaust gas absorption liquid was analyzed by gas chromatography, and the conversion rate of EBHP (ethylbenzene hydroperoxide) was analyzed by iodimetry. The conditions of chromatography are shown in Table 1.

Table 1 Operating conditions of Chromatography

Chromatographic column	Agilent 19091N-133 ( 30m × 250µm × 0.25µm )
Flow rate of H₂	35 mL/min
Flow rate of air	350 mL/min
Flow rate of makeup gas (N₂)	25 mL/min
Heater	270 °C
Column box	250 °C
Heating procedure	Initial temperature: 50 °C
Heating procedure	Heating program: 50-100 °C, 15 °C/min, maintaining for 0 min, 100-250 °C, 20 °C/min, maintaining for 2 min
Split ratio of injection port	30:1
Temperature of FID detector	270 °C

The content of PO was determined by internal standard method. The liquid phase concentration was determined using DMF as the solvent and DT (dioxane) as the internal standard substance. The internal standard curve of PO and DT was determined to be y=0.6985x-0.0046, R²=0.999; the concentration of PO in gas phase absorption liquid was determined using toluene as the internal standard substance, the internal standard curve of PO and toluene was determined to be y=2.161x+0.0002, R²=0.999. $Concentration of PO in liquid phase = (0.6985 \times (A_{PO} / A_{DT}) - 0.0046) \times 0.01 \times dilution ratio,$
A represents the peak area, the same below;
Content of PO in liquid phase = concentration of PO in liquid phase × mass of sample in liquid phase; $Concentration of PO in gas phase = (2.162 \times (A_{PO} / A_{toulene}) + 0.0002) \times mass of toluene;$
$\begin{array}{l} Content of PO in gas phase = concentration of PO in gas phase \times total amount of absorption \\ liquid / amount of sample in gas phase; \end{array}$
$\begin{array}{l} Total production amount of PO = content of PO in gas phase + content of PO in liquid \\ phase; \end{array}$
$\begin{array}{l} Selectivity to PO = total production amount of PO / amount of PO theoretically produced \\ from propylene oxidized by EBHP (ethylbenzene hydroperoxide) \times 100 % . \end{array}$
The conversion rate of EBHP was titrated by iodimetry and measured by a titrator. $\begin{array}{l} Conversion rate of EBHP = (initial value of EBHP - residual amount of EBHP) / initial \\ value of EBHP . \end{array}$
$\begin{array}{l} Residual amount of EBHP = (tritation end point - blank) \times C_{{Na}_{2} S_{2} O_{3}} \times 0.001 \times 0.5 \times 142 \times \\ total amount of liquid sample / sample amount for titration, wherein C_{{Na}_{2} S_{2} O_{3}} is the concentration \\ of sodium thiosulfate . \end{array}$
The silica gel carrier used in the examples or the comparative examples is an irregular blocky C-type silica gel carrier, which is provided by Qingdao GuiChuang Fine Chemical Co., Ltd., and has a silica gel particle size (spherical equivalent diameter) of 0.6-1.1 mm, a specific surface area of 256 m²/g, an average pore diameter of 9.2 nm, a pore volume of 0.94 ml/g, a water absorption rate of 1.12 g water/g of silica gel (saturated water absorption), a Na₂O impurity content of 89 ppm and a Fe₂O₃ impurity content of 327 ppm.
The process conditions for propylene epoxidation to produce propylene oxide in the examples and comparative examples are as follows: the oxidant is ethylbenzene hydroperoxide (EBHP), the reaction tube is a fixed bed reactor with an inner diameter of 24 mm, and the catalyst is loaded in an amount of 10 g; the molar ratio of propylene to EBHP is 5:1, the mass space velocity is 4 hr^-1; the initial reaction temperature is 50 °C, and the reaction temperature is gradually increased according to the conversion rate of EBHP (the conversion rate of EBHP was guaranteed to be >99%).

Example 1

0.36 g of Ce(NO₃)₃ was weighed and dissolved in 33.6 g of distilled water, sprayed onto 30 g of silica gel carrier, to settle for 2 hours and then dried at 80 °C. The product obtained in this step was called auxiliary metal salt modified silica gel carrier A (or referred to as product A or A for short).
As shown in Fig. 1, the silica gel carrier on which Ce(NO₃)₃ was loaded (i.e., product A) was charged into reaction tube 5 and dried at 180 °C for 120 min in N₂ atmosphere, and the linear velocity of N₂ in reaction tube 5 was 1.2 cm/s. Dried A was obtained in this step.
Chemical vapor deposition of TiCl₄: 2.98g of TiCl₄ was added to TiCl₄ vaporization tank 2 which was then heated at a temperature of 137 °C, TiCl₄ vapor was introduced into reaction tube 5 using N₂ to react with the silica gel, the linear velocity of N₂ in reaction tube 5 was 0.5 cm/s, the deposition time was 120 min (the reaction temperature of this step was the same as the drying temperature in the previous step, which was 180 °C); the product obtained in this step was called auxiliary metal salt and TiCl₄ loaded silica gel B (referred to as silica gel B or B for short).
Calcination: the temperature was raised to 500 °C at a heating rate of 2 °C/min, the linear velocity of N₂ in reaction tube 5 was 1 cm/s, and the silica gel B was calcined for 120 min; the product obtained in this step was called auxiliary metal oxide and Ti species loaded silica gel C (or referred to as C for short).
Water washing: 14.1 g of distilled water was added to water and silylanization reagent vaporization tank 3 which was then heated at a temperature of 120 °C, water vapor was introduced into reaction tube 5 using N₂ for water washing the obtained silica gel C, the linear velocity of N₂ in the reaction tube was 1 cm/s and the water washing time was 180 min; the product obtained by water vapor washing was referred to as a Ti-MeO-SiO₂ composite oxide.
Chemical vapor deposition of alkyl silicate: 15g of tetraethyl orthosilicate was added to alkyl silicate vaporization tank 1 which was then heated at a temperature of 166 °C, tetraethyl orthosilicate vapor was introduced into the reaction tube using N₂ to react with the silica gel, the linear velocity of N₂ in the reaction tube was 0.5 cm/s, and the deposition time was 120 min (the reaction temperature of this step was the same as the temperature at which the alkyl silicate vaporization tank was heated, which was 166 °C); the product obtained in this step was called a Ti-MeO-SiO₂ composite oxide D having a silicon-containing compound loaded on the surface of the composite oxide (or referred to as product D);
Calcination: the temperature was raised to 500 °C at a heating rate of 3 °C/min, the linear velocity of air in the reaction tube was 0.5 cm/s, and the product D was calcined for 120 min; a product having a SiO₂ layer coated on the surface was obtained by calcination, the product was called a Ti-MeO-SiO₂ composite oxide having a SiO₂ layer coated on the surface, or is referred to as SiO₂-Ti-MeO-SiO₂.
Silylanization treatment: 4.5 g of hexamethyl disilylamine was added to water and silylanization reagent vaporization tank 3 which was then heated at a temperature of 130 °C, the hexamethyl disilylamine vapor was introduced into the reaction tube using N₂ to react with the silica gel (the silica gel refers to the product obtained by calcination, SiO₂-Ti-MeO-SiO₂), the linear velocity of N₂ in the reaction tube was 1 cm/s, the silylanization temperature was 200 °C, and the silylanization time was 180 min; the obtained catalyst is referred to as TS-C1.
Exhaust gas absorption tank 4 was used for absorbing TiCl₄ that was not loaded on the carrier and HCl gas generated during the calcination and water washing procedure.
The TS-C1 was evaluated. The catalyst was used for propylene epoxidation to produce propylene oxide, operated continuously for 1000 hr, the reaction temperature was raised from the initial 50 °C to 80 °C, and sampled for gas chromatography analysis. The EBHP conversion rate was >99.9%, the highest selectivity to PO reached 96.4%, the average selectivity reached 95.2%. The product was collected for ICP-OES analysis and no catalyst component Ti was found.

Example 2

0.48 g of Pr(NO₃)₃ was weighed and dissolved in 33.6 g of distilled water, sprayed onto 30 g of silica gel carrier, allowed to settle for 2 hours and then dried at 80 °C.
As shown in Fig. 1, the silica gel carrier on which Pr(NO₃)₃ was loaded was charged into a reaction tube and dried at 200 °C for 180 min in N₂ atmosphere, and the linear velocity of N₂ in the reaction tube was 1.6 cm/s.

Chemical vapor deposition of TiCl₄: 3.57g of TiCl₄ was added to a TiCl₄ vaporization tank which was then heated at a temperature of 140 °C, TiCl₄ vapor was introduced into the reaction tube using N₂ to react with the silica gel, the linear velocity of N₂ in the reaction tube was 0.7 cm/s, the deposition time was 180 min (the reaction temperature of this step was the same as the drying temperature in the previous step, which was 200 °C);
Calcination: the temperature was raised to 550 °C at a heating rate of 2 °C/min, the linear velocity of N₂ in the reaction tube was 1.5 cm/s, the calcination lasted for 180 min;
Water washing: 26.7 g of distilled water was added to a water and silylanization reagent vaporization tank which was then heated at a temperature of 140 °C, water vapor was introduced into the reaction tube using N₂ for water washing, the linear velocity of N₂ in the reaction tube was 1.5 cm/s and the water washing time was 180 min;
Chemical vapor deposition of alkyl silicate: 21g of tetraethyl orthosilicate was added to a alkyl silicate vaporization tank which was then heated at a temperature of 170 °C, tetraethyl orthosilicate vapor was introduced into the reaction tube using N₂ to react with the silica gel, the linear velocity of N₂ in the reaction tube was 0.8 cm/s, and the deposition time was 150 min (the reaction temperature of this step was the same as the temperature at which the alkyl silicate vaporization tank was heated, which was 170 °C);
Calcination: the temperature was raised to 550 °C at a heating rate of 3 °C/min, the linear velocity of air in the reaction tube was 0.7 cm/s, the calcination lasted for 60 min;

Silylanization treatment: 3 g of hexamethyl disilylamine was added to a water and silylanization reagent vaporization tank which was then heated at a temperature of 135 °C, hexamethyl disilylamine vapor was introduced into the reaction tube using N₂ to react with the silica gel, the linear velocity of N₂ in the reaction tube was 0.7 cm/s, the silylanization temperature was 200 °C, and the silylanization time was 150 min; the obtained catalyst was referred to as TS-C2.
The TS-C2 was evaluated. The catalyst was used for propylene epoxidation to produce propylene oxide, operated continuously for 1550 hr, the reaction temperature was raised from the initial 50 °C to 85 °C, and sampled for gas chromatography analysis. The EBHP conversion rate was >99.9%, the highest selectivity to PO reached 96.7%, the average selectivity reached 95.1%. The product was collected for ICP-OES analysis and no catalyst component Ti was found.

Example 3

0.6 g of Tb(NO₃)₃ was weighed and dissolved in 33.6 g of distilled water, sprayed onto 30 g of silica gel carrier, allowed to settle for 2 hours and then dried at 80 °C.
As shown in Fig. 1, the silica gel carrier on which Tb(NO₃)₃ was loaded was charged into a reaction tube and dried at 240 °C for 240 min in N₂ atmosphere, and the linear velocity of N₂ in the reaction tube was 2 cm/s.

Chemical vapor deposition of TiCl₄: 4.17g of TiCl₄ was added to a TiCl₄ vaporization tank which was then heated at a temperature of 145 °C, TiCl₄ vapor was introduced into the reaction tube using N₂ to react with the silica gel, the linear velocity of N₂ in the reaction tube was 0.8 cm/s, the deposition time was 200 min (the reaction temperature of this step was the same as the drying temperature in the previous step, which was 240 °C);
Calcination: the temperature was raised to 600 °C at a heating rate of 2 °C/min, the linear velocity of N₂ in the reaction tube was 2 cm/s, the calcination lasted for 200 min;
Water washing: 33.5 g of distilled water was added to a water and silylanization reagent vaporization tank which was then heated at a temperature of 160 °C, water vapor was introduced into the reaction tube using N₂ for water washing, the linear velocity of N₂ in the reaction tube was 2 cm/s and the water washing time was 200 min;
Chemical vapor deposition of alkyl silicate: 27g of tetraethyl orthosilicate was added to a alkyl silicate vaporization tank which was then heated at a temperature of 180 °C, tetraethyl orthosilicate vapor was introduced into the reaction tube using N₂ to react with the silica gel, the linear velocity of N₂ in the reaction tube was 0.9 cm/s, and the deposition time was 180 min (the reaction temperature of this step was the same as the temperature at which the alkyl silicate vaporization tank was heated, which was 180 °C);
Calcination: the temperature was raised to 600 °C at a heating rate of 3 °C/min, the linear velocity of air in the reaction tube was 0.8 cm/s, the calcination lasted for 60 min;

Silylanization treatment: 2.4 g of hexamethyl disilylamine was added to a water and silylanization reagent vaporization tank which was then heated at a temperature of 140 °C, hexamethyl disilylamine vapor was introduced into the reaction tube using N₂ to react with the silica gel, the linear velocity of N₂ in the reaction tube was 0.5 cm/s, the silylanization temperature was 250 °C, and the silylanization time was 120 min; the obtained catalyst was referred to as TS-T3.
The TS-T3 was evaluated. The catalyst was used for propylene epoxidation to produce propylene oxide, operated continuously for 1800 hr, the reaction temperature was raised from the initial 50 °C to 90 °C, and sampled for gas chromatography analysis. The EBHP conversion rate was >99.9%, the highest selectivity to PO reached 97.8%, the average selectivity reached 96.7%. The product was collected for ICP-OES analysis and no catalyst component Ti was found.

Example 4

0.72 g of La(NO₃)₃ was weighed and dissolved in 33.6 g of distilled water, sprayed onto 30 g of silica gel carrier, allowed to settle for 2 hours and then dried at 80 °C.
As shown in Fig. 1, the silica gel carrier on which La(NO₃)₃ was loaded was charged into a reaction tube and dried at 220 °C for 120 min in N₂ atmosphere, and the linear velocity of N₂ in the reaction tube was 2.5 cm/s.

Chemical vapor deposition of TiCl₄: 5.36g of TiCl₄ was added to a TiCl₄ vaporization tank which was then heated at a temperature of 150 °C, TiCl₄ vapor was introduced into the reaction tube using N₂ to react with the silica gel, the linear velocity of N₂ in the reaction tube was 1.35 cm/s, the deposition time was 240 min (the reaction temperature of this step was the same as the drying temperature in the previous step, which was 220 °C);
Calcination: the temperature was raised to 550 °C at a heating rate of 2 °C/min, the linear velocity of N₂ in the reaction tube was 2.5 cm/s, and the calcination lasted for 240 min;
Water washing: 50.7 g of distilled water was added to a water and silylanization reagent vaporization tank which was then heated at a temperature of 180 °C, water vapor was introduced into the reaction tube using N₂ for water washing, the linear velocity of N₂ in the reaction tube was 2.5 cm/s and the water washing time was 240 min;
Chemical vapor deposition of alkyl silicate: 30g of tetraethyl orthosilicate was added to a alkyl silicate vaporization tank which was then heated at a temperature of 200 °C, the tetraethyl orthosilicate vapor was introduced into the reaction tube using N₂ to react with the silica gel, the linear velocity of N₂ in the reaction tube was 1 cm/s, and the deposition time was 180 min (the reaction temperature of this step was the same as the temperature at which the alkyl silicate vaporization tank was heated, which was 200 °C);
Calcination: the temperature was raised to 700 °C at a heating rate of 3 °C/min, the linear velocity of air in the reaction tube was 1 cm/s, the calcination lasted for 30 min;

Silylanization treatment: 1.8 g of hexamethyl disilylamine was added to a water and silylanization reagent vaporization tank which was then heated at a temperature of 150 °C, hexamethyl disilylamine vapor was introduced into the reaction tube using N₂ to react with the silica gel, the linear velocity of N₂ in the reaction tube was 0.6 cm/s, the silylanization time was 150 min; the silylanization temperature was 300 °C, the obtained catalyst was referred to as TS-L4.
The TS-L4 was evaluated. The catalyst was used for propylene epoxidation to produce propylene oxide, operated continuously for 1200 hr, the reaction temperature was raised from the initial 50 °C to 75 °C, and sampled for gas chromatography analysis. The EBHP conversion rate was >99.9%, the highest selectivity to PO reached 96.8%, the average selectivity reached 95.6%. The product was collected for ICP-OES analysis and no catalyst component Ti was found.

Comparative Example 1

0.6 g of Tb(NO₃)₃ was weighed and dissolved in 33.6 g of distilled water, sprayed onto 30 g of silica gel carrier, allowed to settle for 2 hours and then dried at 80 °C.
The silica gel carrier on which Tb(NO₃)₃ was loaded was charged into the reaction tube and dried at 240 °C for 240 min in N₂ atmosphere, and the linear velocity of N₂ in the reaction tube was 2 cm/s.

Chemical vapor deposition of TiCl₄: 4.17g of TiCl₄ was added to a TiCl₄ vaporization tank which was then heated at a temperature of 145 °C, TiCl₄ vapor was introduced into the reaction tube using N₂ to react with the silica gel, the linear velocity of N₂ in the reaction tube was 0.8 cm/s, the deposition time was 200 min (the reaction temperature of this step was the same as the drying temperature in the previous step, which was 240 °C);
Calcination: the temperature was raised to 600 °C at a heating rate of 2 °C/min, the linear velocity of N₂ in the reaction tube was 2 cm/s, and calcination lasted for 200 min;
Water washing: 33.5 g of distilled water was added to a water and silylanization reagent vaporization tank which was then heated at a temperature of 160 °C, water vapor was introduced into the reaction tube using N₂ for water washing, the linear velocity of N₂ in the reaction tube was 2 cm/s and the water washing time was 200 min;

Silylanization treatment: 2.4 g of hexamethyl disilylamine was added to a water and silylanization reagent vaporization tank which was then heated at a temperature of 140 °C, the hexamethyl disilylamine vapor was introduced into the reaction tube using N₂ to react with the silica gel, the linear velocity of N₂ in the reaction tube was 0.5 cm/s, the silylanization temperature was 250 °C, and the silylanization time was 120 min; the obtained catalyst was referred to as TS-B4.
The TS-B4 was evaluated. The catalyst was used for propylene epoxidation to produce propylene oxide, operated continuously for 750 hr, the reaction temperature was raised from the initial 50 °C to 80 °C, and sampled for gas chromatography analysis. The EBHP conversion rate was >99.9%, the highest selectivity to PO reached 97.5%, the average selectivity reached 95.7%. The product was collected for ICP-OES analysis, the content of the catalyst component Ti in the product was about 313 ppm; the Ti content in the fresh catalyst was about 3.42%, the Ti content in the catalyst after evaluation was about 2.61%, and the loss rate reached 23.7%.

Comparative Example 2

30g of silica gel carrier was weighed and charged into the reaction tube and dried at 240 °C for 240 min in N₂ atmosphere, and the linear velocity of N₂ in the reaction tube was 2 cm/s.

Chemical vapor deposition of TiCl₄: 4.17g of TiCl₄ was added to a TiCl₄ vaporization tank which was then heated at a temperature of 145 °C, the TiCl₄ vapor was introduced into the reaction tube using N₂ to react with the silica gel, the linear velocity of N₂ in the reaction tube was 0.8 cm/s, the deposition time was 200 min (the reaction temperature of this step was the same as the drying temperature in the previous step, which was 240 °C);
Calcination: the temperature was raised to 600 °C at a heating rate of 2 °C/min, the linear velocity of N₂ in the reaction tube was 2 cm/s, the calcination lasted for 200 min;
Water washing: 33.5 g of distilled water was added to a water and silylanization reagent vaporization tank which was then heated at a temperature of 160 °C, the water vapor was introduced into the reaction tube using N₂ for water washing, the linear velocity of N₂ in the reaction tube was 2 cm/s and the water washing time was 200 min;
Chemical vapor deposition of alkyl silicate: 27g of tetraethyl orthosilicate was added to a alkyl silicate vaporization tank which was then heated at a temperature of 180 °C, tetraethyl orthosilicate vapor was introduced into the reaction tube using N₂ to react with the silica gel, the linear velocity of N₂ in the reaction tube was 0.9 cm/s, and the deposition time was 180 min (the reaction temperature of this step was the same as the temperature at which the alkyl silicate vaporization tank was heated, which was 180 °C);
Calcination: the temperature was raised to 600 °C at a heating rate of 3 °C/min, the linear velocity of air in the reaction tube was 0.8 cm/s, the calcination lasted for 60 min;

Silylanization treatment: 2.4 g of hexamethyl disilylamine was added to a water and silylanization reagent vaporization tank which was then heated at a temperature of 140 °C, hexamethyl disilylamine vapor was introduced into the reaction tube using N₂ to react with the silica gel, the linear velocity of N₂ in the reaction tube was 0.5 cm/s, the silylanization temperature was 250 °C, and the silylanization time was 120 min; the obtained catalyst was referred to as TS-01.
The TS-01 was evaluated. The catalyst was used for propylene epoxidation to produce propylene oxide, operated continuously for 1500 hr, the reaction temperature was raised from the initial 50 °C to 100 °C, and sampled for gas chromatography analysis. The EBHP conversion rate was >99.9%, the highest selectivity to PO reached 94.6%, the average selectivity reached 92.1%. The product was collected for ICP-OES analysis and no catalyst component Ti was found.

Comparative Example 3:

Chemical vapor deposition of TiCl₄: 4.17g of TiCl₄ was added to a TiCl₄ vaporization tank which was then heated to a temperature of 145 °C, TiCl₄ vapor was introduced into the reaction tube using N₂ to react with the silica gel, the linear velocity of N₂ in the reaction tube was 0.8 cm/s, the deposition time was 200 min (the reaction temperature was the same as the drying temperature in the previous step, which was 200 °C);
Calcination: the temperature was raised to 600 °C at a heating rate of 2 °C/min, the linear velocity of N₂ in the reaction tube was 2 cm/s, and the calcination lasted for 200 min;
Water washing: 33.5 g of distilled water was added to a water and silylanization reagent vaporization tank which was then heated at a temperature of 160 °C, the water vapor was introduced into the reaction tube using N₂ for water washing, the linear velocity of N₂ in the reaction tube was 2 cm/s and the water washing time was 200 min;
Calcination: the temperature was raised to 600 °C at a heating rate of 3 °C/min, the linear velocity of air in the reaction tube was 0.8 cm/s, the calcination lasted for 60 min;

Silylanization treatment: 2.4 g of hexamethyl disilylamine was added to a water and silylanization reagent vaporization tank which was then heated at a temperature of 140 °C, hexamethyl disilylamine vapor was introduced into the reaction tube using N₂ to react with the silica gel, the linear velocity of N₂ in the reaction tube was 0.5 cm/s, the silylanization temperature was 250 °C, and the silylanization time was 120 min; the obtained catalyst was referred to as TS-02.
The TS-02 was evaluated. The catalyst was used for propylene epoxidation to produce propylene oxide, operated continuously for 620 hr, the reaction temperature was raised from the initial 50 °C to 95 °C, and sampled for gas chromatography analysis. The EBHP conversion rate was >99.9%, the highest selectivity to PO reached 93.6%, the average selectivity reached 91.1%; the Ti content in the fresh catalyst was about 3.45%, the product was collected for ICP-OES analysis, the Ti content in the catalyst after evaluation was about 2.56%, and the loss rate reached 25.8%.
The experimental results of the examples and the comparative examples show that the catalysts prepared by the preparation methods of the present invention had good catalyst stabilities during use, the activities and selectivities of the catalysts did not change significantly during the observation time, and the activities were stable; Ti element was not found in the product of each example, indicating that the active component in the catalyst was not lost. It can be seen that the catalysts prepared by the preparation methods of the present invention can reduce the loss of the Ti active centers during use, the catalyst activites were stable, the service lives of the catalysts were improved; and the catalysts had high selectivities to PO.

Claims

A preparation method for an olefin epoxidation catalyst, which comprises the following steps:
(1) loading an auxiliary metal salt onto a silica gel carrier to obtain an auxiliary metal salt modified silica gel carrier A, wherein the auxiliary metal salt is one or more of Ce(NO₃)₃, Pr(NO₃)₃, Tb(NO₃)₃ and La(NO₃)₃; preferably, using a impregnation method to load the auxiliary metal salt onto the silica gel carrier;

(2) carrying out a drying treatment for the A obtained in step (1);

(3) carrying out a chemical vapor deposition for the dried A using a titanium salt vapor, preferably TiCl₄ vapor to obtain a silica gel B on which the auxiliary metal salt and the titanium salt, preferably TiCl₄ were loaded;

(4) calcining the B obtained in step (3) to obtain a silica gel C on which the auxiliary metal salt and Ti species are loaded;

(5) carrying out a water vapor washing for the C obtained in step (4) to obtain a Ti-MeO-SiO₂ composite oxide;

(6) carrying out a vapor deposition for the Ti-MeO-SiO₂ composite oxide using an alkyl silicate vapor to obtain the Ti-MeO-SiO₂ composite oxide D having a silicon-containing compound loaded on the surface of the composite oxide; preferably, the alkyl silicate vapor is tetraethyl orthosilicate vapor;

(7) calcining the D obtained in step (6) to obtain a Ti-MeO-SiO₂ composite oxide having a SiO₂ layer coated on the surface of the composite oxide, which is referred to as SiO₂-Ti-MeO-SiO₂;

(8) carrying out a silylanization treatment for the SiO₂-Ti-MeO-SiO₂ obtained in step (7); wherein "MeO" represents the oxide of the auxiliary metal.
The method according to claim 1, wherein in step (1), using the amount of the metal oxide of the auxiliary metal salt for calculation, the auxiliary metal salt is added in an amount ranging from 0.6-2.4 wt% based on the mass of the silica gel carrier.
The method according to claim 1 or 2, wherein the silica gel carrier used in step (1) is a C-type silica gel, preferably a spherical shape or a block C-type silica gel, more preferably an irregular blocky C-type silica gel;
preferably, the silica gel carrier used in step (1) has a specific surface area of 100-350 m²/g, an average pore diameter of 8-11 nm, a pore volume of 0.7-1.2 ml/g, a Na₂O impurity content of <100 ppm, a Fe₂O₃ impurity content of <500 ppm and a size of a spherical equivalent diameter of 0.5-2 mm.
The method according to any one of claims 1-3, wherein in step (2), the drying temperature is 150-240 °C and drying time is 120 min - 240 min;
preferably, in step (2), using a drying gas to carry out the drying, and the drying gas is a gas that does not react with silica gel, preferably air or nitrogen; more preferably, the drying in step (2) is carried out specifically in a reaction tube, and the flow rate of the drying gas in the reaction tube is preferably 1.0-3.0 cm/s.
The method according to any one of claims 1-4, wherein based on the weight of the silica gel carrier used in step (1), in step (3), Ti is loaded on the silica gel carrier in an amount ranges from 0.1-5.0 wt%, preferably 2.5-4.5 wt%;
preferably, the titanium salt vapor used in step (3) has a temperature of 137 °C - 150 °C;

preferably, the chemical vapor deposition of step (3) is carried out in a reaction tube, the dried A is charged in the reaction tube, an inert gas, preferably N₂ is used to introduce the titanium salt vapor into the reaction tube, the inert gas has a flow rate of 0.05-2.0 cm/s, preferably 0.50-1.35 cm/s in the reaction tube, the temperature of the reaction is 150-300 °C, and the deposition time is 120-240 min.
The method according to any one of claims 1-5, wherein the calcination in step (4) is carried out in N₂ atmosphere, at a calcination temperature ranges from 450-700 °C, preferably 500-600 °C, a calcination time ranges from 30-240 min, preferably 120-180 min, the flow rate of N₂ is 0.05-2.0 cm/s, preferably 1-2.5 cm/s.
The method according to any one of claims 1-6, wherein the water vapor used for water washing in step (5) has a temperature of 100-200 °C, preferably 120-180 °C;
based on the amount of the Ti element in the titanium salt vapor used in step (3), the molar ratio of the water vapor to Ti is 20-150: 1, preferably 50-100: 1, the water washing time is 180-240 min;

the water vapor washing of step (5) is preferably carried out in a reaction tube, water vapor is introduced into the reaction tube using an inert gas, preferably N₂, the inert gas has a flow rate of 1-2.5 cm/s.
The method according to any one of claims 1-7, wherein the alkyl silicate vapor used in step (6) is heated to a temperature of 166-200 °C;
the vapor deposition of step (6) is carried out in a reaction tube, and the alkyl silicate vapor is introduced into the reaction tube using an inert gas, the inert gas is preferably N₂; the flow rate of the inert gas in the reaction tube is 0.05-2.0 cm/s, preferably 0.5-1.0 cm/s, the reaction temperature is 166-200 °C, the deposition time is 120-180 min, and the weight ratio of alkyl silicate to the silica gel carrier used in step (1) is 0.5-1:1.
The method according to any one of claims 1-8, wherein the calcination in step (7) is carried out in air atmosphere at a temperature of 500-700 °C, with a calcination time of 30-120 min, and the flow rate of air is 0.5-1 cm/s.
The method according to any one of claims 1-9, wherein the silylanization reagent used for the silylanization treatment in step (8) is hexamethyl disilylamine, based on the weight of the silica gel carrier used in step (1), hexamethyl disilylamine is used in an amount of 5 wt% - 15 wt%;
preferably, the temperature of hexamethyl disilylamine used in step (8) is 126-150 °C; preferably, the silylanization treatment is carried out in a reaction tube, the silylanization reagent vapor is introduced into the reaction tube using an inert gas, preferably N₂, the flow rate of the inert gas in the reaction tube is 0.5-1 cm/s, the silylanization temperature is 200-300 °C, and the silylanization time is 60-180 min.
Use of the catalyst prepared by the method according to any one of claims 1-10 for catalyzing propylene epoxidation to prepare propylene oxide.
The use according to claim 11, wherein the process conditions for catalyzing propylene epoxidation to prepare propylene oxide are as follows: a reaction temperature of 40-120 °C, a gauge pressure of 2-4.5 MPa, a molar ratio of propylene to ethylbenzene hydroperoxide of 3-10:1 and a mass space velocity of 1-5 h^-1.